Method for installing dynamic, modular, single-lock anterior cervical plate system having assembleable and moveable segments

ABSTRACT

An anterior cervical plating system having modular plate segments that are assembleable to vary the overall length of the plate, moveable to allow and/or cause intersegmental compression of vertebral bodies, and coupled together by a detachable fastener. The plating system includes locking elements for locking only one bone screw to the plate, instrumentation, and method for installation thereof. The plating system is capable of both passive and active dynamization and the ability to produce the former from the latter.

RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.10/160,062, filed Jun. 4, 2002; which claims the benefit of U.S.provisional Application No. 60/296,060, filed Jun. 4, 2001, and U.S.provisional Application No. 60/355,194, filed Feb. 8, 2002; all of whichare incorporated by reference herein.

BACKGROUND

The use of plates, screws, and locks to prevent separation and backingout of screws from the plate, for use on the anterior aspect of thecervical spine to provide alignment and stability as an adjunct tofusion of adjacent vertebral bodies is known in the art. Also known inthe art is that compressive load, within a physiological range across afusion site, is beneficial to the fusion process. Conversely, a failureto maintain a compressive load across a fusion site, or to have a gap inthe fusion construct continuity may lead to a failure to achieve fusioncalled pseudoarthrosis. A primary purpose of the aforementioned cervicalhardware is to provide stability during the healing and fusion process.The fusion process occurs in part through a process called “creepingsubstitution” by which new living bone replaces the dead bone such asthat of a bone graft. The fusion process involves a phase of boneresorption as preliminary to the formation of the new bone. It ispossible then for the bone resorption to result in gaps in thecontinuity of the fusion mass, such that if the hardware is sufficientlyrigid, such as occurs as a result of increasing the strength of thecomponents and constraining the relationship of the screws to the plate,those gaps may persist and increase in size as the hardware holds thebone portions separated rather than allowing those bone portions to movetogether to close those gaps. This holding apart of the bone portions(called distraction) can therefore lead to a failure of fusion(pseudoarthrosis). These rigid systems by a combination of not inducingcompression at the fusion site and of holding the bone portions to befused apart may cause a “distraction pseudoarthrosis.”

Alternative cervical plating systems have attempted to preventdistraction pseudoarthrosis by allowing the vertebral bodies to collapsetowards each other as needed during the fusion process. Generally thishas been done by allowing the bone screws to be free to move relative tothe plate, that is, movement such as sliding, swiveling, rotating, andangulating, independent of whether the screws are prevented fromseparating or backing out of the plates such as by the use of locks.Undesired multidirectional instability can occur in such plating systemsthat is counter to the very purpose of such hardware which is toincrease or provide for stability.

Another approach to solving this problem has been to attach by screws ablock to each of the vertebral bodies to be fused and then to allowthose blocks to slide up and down on a pair of rods. Each of theseconstructs have in common that they sacrifice stability, the ability tohold the bones to be fused rigidly in place and prevent undesiredmotion; for the ability to allow, but not cause the vertebral bodies tocollapse.

There exists therefore a need for an improved anterior cervical platingsystem that is: (1) sufficiently rigid to maintain the desired alignmentof the vertebral bodies to be fused; (2) capable of inducing compressiveload across the fusion site; and/or (3) capable of allowing for themotion of the vertebral bodies towards each other to prevent or to closeany gaps in the continuity of the fusion construct, while still beingcapable of preventing motion in all other directions. When similarchallenges have been faced at other skeletal locations, the solutioninvolved anchoring the bone screws through the far cortex of the boneportions to be joined, in effect anchoring the screws in such a way asto make it possible for the screws to force movement of the plates. Inthe cervical spine anteriorly, however, it has been found to be highlyundesirable to drive the bone screws through the far cortex of thevertebral bodies, as this is where the spinal cord is located. Thereremains therefore a need for an improved cervical plating system as justdescribed that does not require that the bone screws penetrate the farcortex to achieve the desired purpose as described.

The size of the vertebral bodies and the spacing between the vertebralbodies varies from patient to patient. The height of the vertebralbodies and the discs therebetween may vary level by level even in thesame person. Thus, a plate of correct length does not necessarily havebone screw receiving holes correctly positioned to overlie the vertebralbodies in accordance with the spacing of the vertebral bodies to whichthe plate is to be applied. As a result, conventional plating systems ofthe past had to be manufactured in many different lengths and spacingconfigurations which were nevertheless fixed in an attempt to provideplates for many, though still possibly not all, of the various sizes andspacings of the vertebral bodies to which the plate was to be applied.For example, in a multi-segment plate the length of the plate would needto correspond to the overall length of the vertebral bodies to be joinedand actual distances therebetween and the screw holes of the platearranged to overlie the vertebral bodies. In order to cover the possiblerange of sizes, health care facilities would need to carry a largeinventory of different sizes of plates, in some cases as many as sixtydifferent sized plates would be needed. Such a large inventory is anexpensive undertaking and still worse, facilities with a high caseloadneed to invest in more than one of each plate size to provide for thepossibility of overlapping demand for the same plate size. Facilitieswith lower caseloads may find it prohibitively expensive to stock aninventory of plates sufficient to cover the range of possible sizes andthus might not be able to afford to stock a set at all or have less thanall sizes of plates needed for all cases. Manufactures cannot afford toplace a set of plates on consignment in facilities with low caseloads asthe number of sales would not cover the carrying costs of the plates.

There exists therefore a need for an improved anterior cervical platingsystem that (1) allows for the overall adjustability of the length ofthe plate; (2) allows for variations in spacing between the bone screwreceiving holes of the plate portions corresponding to the attachmentpoint of the plate to the vertebral bodies; (3) reduces the requisiteplate inventory; and (4) can avoid or prevent distractionpseudoarthrosis without itself introducing multidirectional instability.

SUMMARY OF THE INVENTION

The present invention is a dynamic, modular anterior cervical platingsystem including a plate comprising assembleable segments in moveablerelationship to each other adapted to allow for the overalladjustability of the length of the plate and for variations in theintersegmental spacing of the bone screw receiving holes, create and/orstore a compressive load across a disc space between two adjacentvertebral bodies to be fused, and/or allow motion of the vertebralbodies toward each other to prevent or close gaps in the continuity of afusion construct, while preferably preventing motion in all otherdirections when in use. As used herein, a spinal fusion segment isdefined as two vertebral bodies with an intervertebral implant, made ofbone or an artificial material, in the disc space therebetween. As usedherein, a fusion construct is defined as a spinal fusion segment plusthe hardware, such as a plate and screws for example.

The ability to permit the movement of adjacent vertebral bodies towardone another is referred to herein as “dynamization.” Dynamization may be“passive” allowing the plate to shorten when a shortening force, such asa compressive load is applied. Dynamization may be “active” wherein theplating system stores energy to induce shortening of the fusionconstruct should the opportunity present. The present invention platingsystem may passively dynamize, actively dynamize, provide a combinationof both, as well as convert and store certain compressive stressesencountered during the healing phase as will be more fully describedherein.

The plate segments can also be moved to vary the spacing between theplate segments as well as the overall length of the plate so that thesize of the plate may be adjusted to correspond to a range of sizes andspacing of the adjacent vertebral bodies to which the plate is beingapplied thereby greatly reducing the inventory of plate sizes needed.The moveable plate segments combine to form the plate. Each platesegment is attached to a vertebral body to be fused by at least one bonescrew and preferably a pair of bone screws, which when inserted, arepreferably prevented from backing out of the plate by locking elements,one locking element per bone screw.

The paths of the bone screws through the plate may be fixed or variable.If the paths are variable, they may be more or less stable depending onhow resistant to motion the screws are relative to the plate when thescrews are locked to the plate. To the extent that screws aresufficiently stable in relation to the plate to make use of the presentinventive teaching, these screw, plate, and lock combinations orvariations thereon are also within the broad scope of the presentinvention.

In a first embodiment of the present invention, after each of thesegments of the plate are attached to a respective one of the vertebralbodies to be fused, the plate is capable of movement from a first orelongated position to a second or shorter position, a process generallyreferred to as “passive dynamization”— that is the ability of the systemto allow the plated spinal segment to shorten in response to unmetcompressive loads to allow for the bone portions to be fused to moveclose together to restore contact. A preferred embodiment of thispresent invention is capable of allowing for this passive dynamizationwhile preventing undesirable motions along and around all axes otherthan the motion along the longitudinal axis of the plate.

In another preferred embodiment of the present invention, the platesegments are articulated in such a way that even the one freedom ofmovement that is along the longitudinal axis of the plate is selectivelylimited to the desired passive dynamization—that is shortening of theplate construct. This preferred embodiment of the present invention willshorten as required to maintain loaded contact of the bone portions tobe fused, and if challenged, resist any forces such as those that wouldaccompany cervical extension that would distract or destabilize theconstruct by elongating it. A further benefit of this embodiment is itsability to store and impart a compressive load across the fusion sitereferred to herein as “active dynamization” wherein energy stored in thesystem shortens the plate construct if conditions permit. This load canbe applied by the surgeon at the time of surgery and/or be producedduring the healing phase by harnessing the compressive loads such asoccur randomly with neck motion. Compressive load within a physiologicalrange has been shown to have a beneficial effect on the healing of bone.The induction of a compressive load across vertebral bodies to be fused,induces bone growth and when bone resorption occurs at the interface ofthe graft or implant and the vertebral bodies to be joined, thosevertebral bodies are urged to move closer together, thus avoiding theformation of a gap therebetween and thereby acting to mitigate againstpseudoarthrosis.

Alternatively, various embodiments of the present invention allow thesurgeon to induce a desired amount of preload (compressive force) acrossthe fusion site and to permit a desired amount of shortening of theconstruct—“active dynamization” should the opportunity occur; and yetlock the system to prevent any further shortening as might present arisk of deformity or be otherwise undesirable. Such a system urges thebone portions closer together.

In a preferred embodiment, a pre-load force can be applied to the platesegments such that while the plate segments may undergo no added motioninitially, there is a selective force applied to the plate segments andthe plate segments are capable of motion in only one direction, suchthat should resorption occur at one of the fusion interfaces then theplate segments are not only free to move in a direction toward oneanother, and only in that direction, but are also urged to do so torelieve that preload force. Such a system urges the vertebral bodiestogether over time as resorption permits.

Alternatively, in another embodiment of the plate of the presentinvention, a desired amount of preload (compressive force) may beinduced across the fusion site to permit active dynamization should theopportunity occur, without locking the system such that after activedynamization is exhausted (if exhausted), then the plate will stillallow passive dynamization to occur thereafter.

In another embodiment of the present invention, the plate includes astructural feature such as a groove, recess, slot, cam, or pivot, withinits physical perimeter to engage a tool to cooperatively move segmentsof the plate towards each other. These embodiments of the presentinvention may be adapted to allow for passive, active, or active pluspassive dynamization, and when used to store compressive load to allowfor or prevent further motion thereafter. In a preferred version of thethis embodiment, the structural feature contained within the plate forgenerating the compressive load and/or shortening the plate, may alsoserve as the locking mechanism to limit the amount of further shorteningpossible.

Various embodiments of the plating system of the present inventionprovide one or more of the following advantages:

1. Reduces the requisite plate inventory as each plate may cover a rangeof sizes. The plate of the present invention includes multiple segmentsof varying sizes wherein the segments are adapted to be assembledaccording to the size and spacing of the vertebral bodies to which theplate is to be applied. The plate may have its segments moved so thatthe spacing between the plate segments may be further adjusted so as tocorrespond to the actual distances between the vertebral bodies to befused in a multi-segment construct for a more precise fit. The height ofthe discs and the vertebral bodies may vary level by level even in thesame person. Thus, the ability to adjust the distances between thesegments of the plates that correspond to the attachments to thosevertebral bodies allows for a more precise fit of the plate to the spinewith a reduced inventory of the number of plates required to do so.

2. It is possible to precisely contour each segment separately.

3. Reduces the risk that the plate construct will be discovered to betoo short or too long after the attachment process has commenced.

4. It is possible to compress and dynamize levels selectively.

5. The fasteners that link the segments can be tightened to lock thesegments after they are compressed or, alternatively, can allow forfurther motion of the plate segments together.

6. The same hardware can provide for passive dynamization or be rigidlyfixed depending on the fasteners used to link plate segments.

7. The system can allow for passive dynamization, active dynamization,the combination of passive and active dynamization, or can convert bodymotion into active dynamization.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded top perspective view of a plate, a fastener, and alocking element in accordance with a preferred embodiment of the presentinvention.

FIG. 2 is an exploded bottom perspective view of the plate, fastener,and locking element of FIG. 1.

FIG. 3 is a top plan view of the plate, fastener, and locking element ofFIG. 1.

FIG. 4 is a bottom plan view of the plate, fastener, and locking elementof FIG. 1.

FIG. 5 is an end view of the plate of FIG. 1.

FIG. 6 is a side elevation view of the plate of FIG. 1.

FIG. 7 is a partial cross sectional view of the plate of FIG. 1.

FIG. 8 is an enlarged fragmentary view of the plate of FIG. 1 and analternative embodiment of a fastener in accordance with the presentinvention.

FIG. 9 is an enlarged fragmentary cross sectional view of an embodimentof the ratchetings in the upper and lower portions of the plate of FIG.1 in a first position.

FIG. 10 is a fragmentary cross sectional view of FIG. 9 in a secondposition.

FIG. 11 is an enlarged fragmentary cross sectional view of a preferredembodiment of the ratchetings in the upper and lower portions of theplates of the present invention in a first position.

FIG. 12 is a fragmentary cross sectional view of FIG. 11 in a secondposition.

FIG. 13 is a top perspective view of the plate and fastener of FIG. 1and instrumentation for compressing the plate and instrumentation forlocking the fastener in accordance with a preferred embodiment of thepresent invention.

FIG. 14 is a top plan view of the plate and fastener of FIG. 1 in acompressed state with the instrumentation of FIG. 13 shown in crosssection engaging the ends of the plate to compress the plate in thedirection of the arrows and with the instrumentation engaging thefastener.

FIG. 15 is a partial cross sectional view along line 15—15 of FIG. 14.

FIG. 16 is a top perspective view of a plate, a fastener, and a lockingelement in accordance with another preferred embodiment of the presentinvention.

FIG. 17 is a top plan view of the plate and fastener of FIG. 16.

FIG. 18 is a top plan view of the plate of FIG. 16 in an elongated stateand a fastener.

FIG. 19 is a bottom plan view of the plate and fastener of FIG. 16.

FIG. 20 is a partial cross sectional view along line 20—20 of the plateof FIG. 17.

FIG. 21 is an exploded top perspective view of the plate, fastener, andlocking element of FIG. 16.

FIG. 22 is an exploded bottom perspective view of the plate and fastenerof FIG. 16.

FIG. 23 is a top plan view of the plate and fastener of FIG. 16 and apartial fragmentary perspective view of an instrument for compressingthe plate and securing the fastener in accordance with another preferredembodiment of the present invention.

FIG. 24 is an enlarged cross sectional view of the plate of FIG. 16 withthe instrument of FIG. 23 engaging the fastener and positioned withinthe plate.

FIG. 25 is a fragmentary top plan view of the plate of FIG. 16 in anelongated state with the instrument of FIG. 23 shown in cross sectionengaging the fastener and positioned within the plate.

FIG. 26 is a fragmentary top plan view of the plate of FIG. 16 in acompressed state with the instrument of FIG. 23 shown in cross sectionengaging the fastener and positioned within the plate to rotate thefastener in the direction of the arrow to compress the plate.

FIG. 27 is an exploded top perspective view of a plate, a fastener, anda locking element in accordance with another preferred embodiment of thepresent invention.

FIG. 28 is a cross sectional view transverse to the longitudinal axis ofthe plate of FIG. 27.

FIG. 29 is a top plan view of a plate, fasteners, and a locking elementin accordance with another preferred embodiment of the presentinvention.

FIG. 30 is an exploded top perspective view of the plate, fasteners, andlocking element of FIG. 29.

FIG. 31 is an exploded bottom perspective view of the plate, fasteners,and locking element of FIG. 29.

FIG. 32 is a top plan view of the plate, fasteners, and locking elementof FIG. 29.

FIG. 33 is a bottom plan view of the plate, fasteners, and lockingelement of FIG. 29.

FIG. 34 is a side elevation view of the plate of FIG. 29.

FIG. 35 is a partial cross sectional view along the longitudinal axis ofthe plate of FIG. 29.

FIG. 36 is a top plan view of the plate in an elongated position,fasteners, and locking element of FIG. 29.

FIG. 37 is a top perspective view of the plate of FIG. 29 and anotherpreferred embodiment of instrumentation for compressing the plate andinstrumentation for locking the fastener in accordance with the presentinvention.

FIG. 38 is a top plan view of the plate of FIG. 29 in a compressed statewith the instrumentation of FIG. 37 shown in cross section engaging theends of the plate to compress the plate in the direction of the arrows,an alternative embodiment of instrumentation for engaging anintermediary portion of the plate to compress the plate in the directionof the arrows in dotted line, and instrumentation engaging the fastenerand positioned within the plate.

FIG. 39 is a side elevation view of the plate of FIG. 38 with theinstrumentation shown in partial fragmentary, hidden line, and crosssectional views.

FIG. 40 is an exploded top perspective view of a plate, fasteners, andlocking element in accordance with another preferred embodiment of thepresent invention.

FIG. 41 a is an enlarged fragmentary cross sectional view of a lockingelement and bone screw in accordance with a preferred embodiment of thepresent invention.

FIG. 41 b is an enlarged fragmentary cross sectional view of a lockingelement and bone screw in accordance with another preferred embodimentof the present invention.

FIG. 41 c is an enlarged fragmentary cross sectional view of a lockingelement and bone screw in accordance with yet another embodiment of thepresent invention.

FIG. 41 d is an enlarged fragmentary cross sectional view of the lockingelement and bone screw of FIG. 41 c in an angled position.

FIG. 41 e is an enlarged fragmentary cross sectional view of aself-locking bone screw in accordance with a further embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE DRAWINGS

Reference will now be made in detail to the present preferredembodiments (exemplary embodiments) of the invention, examples of whichare illustrated in the accompanying drawings. Wherever possible, thesame reference numbers will be used throughout the drawings to refer tothe same or like parts.

The present invention is for use in the cervical spine wheredynamization is highly desired to prevent distraction pseudoarthrosisand to maintain a compressive load across the fusion interfaces. Thepresent invention in one preferred embodiment is directed to a cervicalplate generally having at least two movable segments that are attachedto the vertebral bodies to be fused and connected in such a way as topermit dynamization of the vertebral bodies preferably along thelongitudinal axis of the plate. The movement of the segments relative toone another may be accompanied by a reduction in the overall length ofthe plate.

FIGS. 1–7 show a preferred embodiment of a cervical plate 100 inaccordance with the present invention. Plate 100 is preferably formed ofa first segment 102 and a second segment 104 in moveable relationship toone another. First and second segments 102, 104 can be of variouslengths and/or configurations such that when the segments are assembledpreferably overlapping at least in part, plates of various lengthsand/or configurations can be formed to cover a range of sizes. First andsecond segments 102, 104 can be of the same or different lengths and canbe coupled to each other or to an intermediate segment as shown in FIGS.29–40 and described below in connection with other preferred embodimentsof the present invention. The overall length of plate 100 and thespacing of segments 102, 104 can be adjusted by moving segments 102, 104relative to one another.

A detachable fastener 106 couples together first and second segments102, 104. Fastener 106 is configured to be detachably attached to atleast one of first and second segments 102, 104 to permit the assemblyof two or more segments. Fastener 106 is detachable to permit completeseparation of first and second segments 102, 104 from one another andassembly of the segments as desired. As used herein, “detachablefastener” is defined as a fastener that once attached is meant to beremoved and then reattached. As shown in FIG. 7, fastener 106, forexample, may be embodied in the form of a screw having a head 108 and ashaft 112 having a thread 116.

As shown in FIG. 8, in another preferred embodiment fastener 106′ may beconfigured to be tightened to only one of first and second platesegments 102, 104 so as to permit movement of first and second segments102, 104 relative to one another when fastener 106′ is fully tightened.For example, fastener 106′ may have a shoulder 110 adapted to bear uponsecond segment 104 as indicated by arrow C. Shoulder 110 is dimensionedso as to create a gap 111 between head 108′ and first segment 102 so asto still permit a specific and desired motion of first and secondsegments 102, 104 relative to one another when fastener 106′ is fullytightened. The limited motion of first and second segments 102, 104relative to one another provides for dynamization of the spinal segmentto be fused in that those vertebral bodies are allowed to move closertogether to maintain contact.

As shown in FIGS. 1 and 2, first segment 102 preferably has an uppersurface 118, a lower surface 120, a medial portion 122, and an end 124.First segment 102 preferably includes bone screw receiving holes 126proximate end 124. Bone screw receiving hole 126 is preferablyconfigured to receive a single bone screw or the bone screw receivingholes also may be configured to receive more than one bone screw. By wayof example only and not limitation, a bone screw receiving hole may bein the form of a slot sized to receive at least two bone screws.

Preferably, at least two of bone screw receiving holes 126 may beoriented in plate 100 to overlie the anterior aspect of a singlecervical vertebral body adjacent a disc space to be fused, though theinvention is not so limited. For example, a first pair of bone screwreceiving holes 126 may be configured to overlie the anterior aspect ofa first cervical vertebral body adjacent a disc space to be fused and atleast a second pair of bone screw receiving holes 126 may be oriented inplate 100 to overlie the anterior aspect of a second cervical vertebralbody adjacent the disc space to be fused.

Bone screw receiving hole 126 may, though need not be, configured toform an interference fit with at least a portion of the trailing end ofa properly dimensioned bone screw to be received therein. Bone screwreceiving holes 126 may be configured, for example only, so that atleast one of bone screw receiving holes 126 may hold a bone screw in afixed relationship to the plate or may hold a bone screw in a moveablerelationship, such as a variable angular relationship, described below.By way of example only and not limitation, bone screw receiving hole 126may have a reduced dimension proximate lower surface 120 of segment 102to form a seat 127. Seat 127 may have a surface adapted to contact atleast a portion of a bone screw inserted therein. The surface may be atleast in part planar, at least in part curved, or have any otherconfiguration suitable for contacting at least a portion of a bonescrew.

End 124 of first segment 102 may also include a tool engagement area 128adapted to cooperatively engage instrumentation for holding plate 100and instrumentation for moving first and second segments relative to oneanother to induce a desired amount of compressive force across thefusion sites and to permit a desired amount of shortening of plate 100.Medial portion 122 preferably has a fastener receiving opening 130adapted to accommodate fastener 106 to couple first and second segments102, 104 to one another.

Fastener receiving opening 130 is preferably configured to permitselected movement of fastener 106 therein and to permit selected motionof first and second segments 102, 104 along the longitudinal axis ofplate 100. Fastener receiving opening 130 may include a shoulder 132recessed from upper surface 118 of first segment 102 adapted to contactthe underside of head 108 of fastener 106 in the tightened position toprevent movement of first and second segments 102, 104 relative to oneanother. Alternatively, if a fastener 106′ is used, shoulder 110contacts second segment 104 and the underside of head 108′ is positionedrelative to shoulder 132 to permit movement of first and second segments102, 104 relative to each other along the longitudinal axis of the platewhen in the tightened position providing for dynamization of thevertebral bodies to be fused to occur, if needed. Fastener 106 andfastener receiving opening 130 preferably cooperate to prevent completeseparation of first and second segments 102, 104 from one another whenfastener 106 is installed. For example, fastener receiving opening 130may be configured to prevent head 108 of fastener 106 from passingtherethrough.

Lower surface 120 of first segment 102 includes a tab receiving recess134 for receiving a tab 136 described below.

Second segment 104 has an upper surface 138, a lower surface 140, amedial portion 142, and an end 144. Second segment 104 preferably hasbone screw receiving holes 126 proximate end 144. End 144 may alsoinclude a tool engagement area 146 adapted to cooperatively engageinstrumentation for holding plate 100 and instrumentation for movingfirst and second segments 102, 104 relative to one another to induce adesired amount of compressive force across the fusion site and to permita desired amount of shortening of plate 100. Medial portion 142preferably includes a fastener receiving opening 148 for receiving aportion of fastener 106. As first and second segments of plate 100 aremodular and assembleable, fastener receiving opening 148 is configuredto permit detachable attachment of fastener 106.

Fastener receiving opening 148 preferably has a thread 150 adapted toengage with thread 116 of fastener 106. The threaded engagement offastener 106 to fastener receiving opening 148 permits first segment 102and second segment 104 to be attached to each other when fastener 106 issufficiently rotated and tightened. As fastener 106 is rotated further,first and second segments 102, 104 are secured together and locked anddo not move relative to each other. Alternatively, if fastener 106′shown in FIG. 8 is used in the tightened position, first and secondsegments 102, 104 are capable of moving relative to each other.

Lower surfaces 120, 140 of first and second segments 102, 104 arepreferably at least in part concave along at least a portion of thelongitudinal axis of the plate, may be bi-concave at least in part, thatis, concave along the longitudinal axis of plate 100 and concavetransverse to the longitudinal axis of the plate, or may have any shapesuitable for the intended purpose transverse to the longitudinal axis ofthe plate. A person skilled in the art will appreciate that plate 100may be adapted for other curvatures or have no curvature withoutdeparting from the intended purpose within the broad scope of thepresent invention. Lower surfaces 120, 140 are preferably adapted tocontact at least a portion of the vertebral bodies to be fused and maybe configured to conform to the anterior aspect of at least a portion ofthe vertebral bodies.

Second segment 104 preferably includes a tab 136 extending from medialportion 142. Tab 136 is configured to cooperatively engage a tabreceiving recess 134 in the lower surface 120 of first segment 102. Tab136 acts as a spring to maintain first and second segments 102, 104aligned along the longitudinal axis of plate 100. Tab 136 also functionsto limit movement of first segment 102 in a direction transverse tolongitudinal axis of plate 100 to prevent end 124 from dropping downbeyond a desired position. This limited movement of first segment 100prevents medial portion 122 of first segment 102 from lifting away frommedial portion 142 beyond a desired position, so that ratchetings 152are not overly separated and rendered less effective as described inmore detail below. It is appreciated that other configurations ofsegments 102, 104 are possible to hold apart segments 102, 104 and tolimit movement of the segments in a direction transverse to thelongitudinal axis of the plate. For example, the longitudinal curvaturesof first and second segments 102, 104 can be slightly different tospring apart segments 102, 104. For example, the radius of curvature ofthe lower surface of segment 102 may be different that the radius ofcurvature of the upper surface of segment 104.

At least a portion of lower surface 120 of first segment 102 and uppersurface 138 of second segment 104 are preferably configured tointerdigitate with one another to permit selected adjustment of thelength of plate 100. For example, lower surface 120 and upper surface138 may include a surface configuration, such as ratchetings 152,configured to cooperatively interdigitate to permit selected andsequential movement along the longitudinal axis of plate 100. Theratchetings are preferably biased to allow movement in one preferreddirection along the longitudinal axis of the plate so as to allowshortening of the plate and resist lengthening of the plate.

FIGS. 9 and 10 show an embodiment of ratchetings having a configurationthat is useful if no movement of first and second segments 102, 104 isdesired after fastener 106 is tightened. A preferred angularrelationship of the cross section of ratchetings 152 a is a 45-45-90degree triangular relationship. As shown in FIG. 9, in a first position,the peaks and valleys of ratchetings 152 a are cooperatively mating.Ratchetings 152 a permit for the fixed positioning of first and secondsegments 102, 104 relative to one another to create a selected length ofplate 100. As shown in FIG. 10, the peaks and valleys are separated topermit movement of the first and second segments in the directions ofthe arrows along the longitudinal axis of plate 100. In order for firstand second segments 102, 104 to move relative to one another, there mustbe sufficient freedom of movement for the segments to move apart inorder to clear the height of the peaks of ratchetings 152 a.Accordingly, in a preferred embodiment fastener 106 is configured tohave at least one position that permits movement of the first and secondsegments along the longitudinal axis of plate 100 as well as along anaxis transverse to the longitudinal axis of plate 100 such thatratchetings 152 can move apart. Fastener 106 can be tightened to asecond position to resist or prevent movement of segments 102, 104relative to one another. For example, movement of segments 102, 104 canbe resisted in a direction along at least a portion of the longitudinalaxis of plate 100.

FIGS. 11 and 12 show another preferred embodiment of ratchetings 152 bhaving a forward-facing configuration for permitting movement in asingle direction. The configuration of ratchetings 152 b is useful whenmovement of first and second segments 102, 104 is desired to permitfurther shortening of the plate. A preferred angular relationship of thetriangular cross section of ratchetings 152 b is a 30-60-90 degreetriangular relationship. As shown in FIG. 12, due to the forward facingangle of ratchetings 152 b, sliding movement of first and secondsegments 102, 104 in the direction, as indicated by the arrow, along thelongitudinal axis of plate 100 is facilitated by the ramped surface 154.In contrast, sliding movement in the opposite direction is restricted byvertical wall 156. Movement of segments 102, 104 is limited to a singledirection with ratchetings 152 a and by limiting the separation ofsegments 102, 104 along an axis transverse to the longitudinal axis ofplate 100 with fastener 106 or 106′.

In a preferred embodiment, fastener 106 or 106′ is configured to have atleast one position that permits movement of first and second segments102, 104 in both directions along the longitudinal axis of plate 100 aswell as along an axis transverse to the longitudinal axis of plate 100such that ratchetings 152 b can move apart. For example, in a firstposition fastener 106 can be less than fully tightened to plate 100 asdesired by the surgeon to permit movement of first and second segmentsrelative to each other. Fastener 106′ can further have a second positionthat permits movement of segments 102, 104 relative to one another onlyin a single direction along the longitudinal axis of plate 100 andlimits movement along an axis transverse to the longitudinal axis ofplate 100. Therefore, plate 100 can be shortened if the distance betweenthe two adjacent vertebral bodies decreases, even after plate 100 isinstalled, so that the vertebral bodies are not held apart by plate 100,to prevent the occurrence of pseudoarthrosis. One of the benefits of aforward-facing configuration of ratchetings 152 b is the ability tostore and impart a compressive load across the fusion site. Thecompressive load stored may be applied by the surgeon and/or compressiveloads that occur randomly with neck motion during the healing phase.First and second segments 102, 104 may be pre-adjusted to correspond tothe appropriate size and spacing of the adjacent vertebral bodies to befused prior to placement of plate 100 against the vertebral bodies bymoving first and second segments 102, 104 relative to one another whilefastener 106 is only partially tightened for the purpose ofappropriately adjusting the length of the plate. Then, fastener 106 maybe further tightened to secure first and second segments 102, 104 in thedesired position.

With appropriate embodiments of the plates described herein, the surgeonmay induce a desired amount of “preload,” or compressive force acrossthe fusion site after plate attachment by moving first and secondsegments 102, 104 toward one another to shorten the length of plate 100as desired. Inducing a preload enhances fusion by maintaining acompressive force between adjacent vertebral bodies and reducing thechance that gaps might develop as new living bone replaces the dead boneduring the fusion process.

FIGS. 13–15 show a preferred embodiment of instrumentation 200 forcompressing and locking plate 100. Instrumentation 200 has a handle 202with a pair of tongs 204, 206 in moveable relationship to each. Tongs204, 206 are configured to cooperatively engage ends 124, 144 of firstand second segments, 102, 104, respectively. Instrumentation 200 may beused to hold and position plate 100 in a desired position at the fusionsite during at least a portion of the procedure for installing plate100. Any instrument capable of engaging the plate so as to serve theintended purpose would be within the scope of the instrumentation andmethod of the present invention. As an example only, methods andinstrumentation for installing plates to the cervical spine, including apilot hole forming punch to create bone screw receiving holes in thevertebral bodies coaxially aligned with the bone screw receiving holeswith the plate, are taught and described by Michelson in U.S. Pat. No.6,193,721 (the '721 patent), incorporated by reference herein. Aftersegments 102, 104 have been attached to the adjacent vertebral bodieswith an appropriate fastening element, such as bone screws, instrument200 can be used to move segments 102, 104 toward one another to shortenthe length of plate 100 and create a compressive load across the discspace. After the desired length of plate 100 is achieved, an instrument208 having a head 210 configured to cooperatively engage fastener 106 isused to tighten fastener 106 to secure first and second segments 102,104 in a desired position. When in a secured position, segments 102, 104may maintain a compressive load across the disc space if desired. Head210 of instrument 208 may have a hex-shaped configuration.

FIGS. 16–22 show another preferred embodiment of a cervical plate 300having an internal compression mechanism in accordance with the presentinvention. Plate 300 is similar to plate 100 except that fastenerreceiving opening 330 and fastener 306 function as part of a mechanismto move first and second segments 302, 304 relative to one another tochange the length of plate 300 to generate a compressive load across thedisc space between two adjacent vertebral bodies to be fused. Fastenerreceiving opening 330 includes instrument pin receiving recesses 362 aand 362 b for cooperating with the pin of an instrument 400 (describedbelow) for moving first and second segments 302, 304 relative to oneanother. In addition, instead of a tab 136, plate 300 has pins 358 andtracks 360 to maintain first and second segments 302, 304 aligned alongthe longitudinal axis of plate 300.

As shown in FIGS. 20–22, first segment 302 preferably has two pins 358depending therefrom for engagement in corresponding tracks 360 in secondsegment 304. Pins 358 slideably engage tracks 360, respectively, andtravel therein when first and second segments 302, 304 are movedrelative to one another. Tracks 360 are staggered along the length ofmedial portion 342 and pins 358 are staggered along the length of medialportion 322 to maintain first and second segments 302, 304 aligned alongthe longitudinal axis of plate 300. It is appreciated that any plateconfiguration to achieve the intended purpose of maintaining first andsecond segments 302, 304 aligned along the longitudinal axis of theplate would be within the scope of the present invention.

FIGS. 23–26 show a preferred embodiment of instrumentation 400 used forcompressing and locking plate 300. Instrumentation 400 has a working end402 configured to cooperatively engage fastener receiving opening 330and fastener 306. After segments 302, 304 have been attached to theadjacent vertebral bodies with an appropriate fastening element, such asbone screws, instrument 400 can be used to move segments 302, 304 towardone another to shorten the length of plate 300, create a compressiveload across the disc space, and concurrently tighten fastener 306 (ifdesired) to secure first and second segments 302, 304 in a preferredposition. Working end 402 of instrument 400 preferably has a driverportion 404 configured to cooperatively engage driver receiving opening364 in fastener 306. Driver portion 404 is preferably hex-shaped.Working end 402 preferably has a pin 406 extending therefrom anddisplaced from driver portion 404 to engage one of pin receivingrecesses 362 a and 362 b, respectively, when driver portion 404 isengaged with driver receiving opening 364 in fastener 306. With driverportion 404 engaging fastener 306 and pin 406 inserted in pin receivingrecess 362 b as shown in FIG. 25, instrument 400 rotates fastener 306 inthe direction of arrow A as shown in FIG. 26 to move first segment 302toward second segment 304 in the direction of arrow B to reduce thelength of plate 300 and can if desired concurrently tighten fastener306. The configuration of plate 300 provides for an internal compressionmechanism that can be operated by a driver instrument eliminating theneed for an externally applied compression apparatus for shorteningplate 300 and creating a compressive load.

FIGS. 27–28 show another preferred embodiment of a cervical plate 500 inaccordance with the present invention. Plate 500 is similar to plate 100except that first segment 502 is configured to receive at least aportion of second segment 504 therein in a tongue and grooveconfiguration. As shown in FIG. 28, first segment 502 preferably has aC-shaped cross section and second segment 504 preferably has a T-shapedcross section. The configurations of segments 502, 504 in thisembodiment of the present invention keep segments 502, 504 aligned alongthe longitudinal axis of plate 500 and limit movement of segments 502,504 in a direction generally transverse to the longitudinal axis ofplate 500. A person of ordinary skill in the art would appreciate thatother configurations of cooperatively engaging first and second segments502, 504 are possible without departing from the intended purpose withinthe broad scope of the present invention.

FIGS. 29–36 show another preferred embodiment of a cervical plate 600 inaccordance with the present invention. Plate 600 is similar to plate 100except that it is configured for use across two levels of the cervicalspine. In addition to the elements of plate 100, plate 600 furtherincludes an intermediate third segment 666 between first and secondsegments 602, 604. Third segment 666 has a first end 668 configured tocooperatively engage first segment 602. Third segment 666 has a secondend 670 configured to cooperatively engage second segment 604. Thirdsegment 666 and first and second segments 602, 604 are articulated andcan be moved to vary the spacing between the bone screw receiving holesof the plate segments as well as the overall length of the plate. Thirdsegment 666 can be made of different lengths and/or configurations tovary the distance between first and second segments 602, 604 to furthervary the spacing between the bone screw receiving holes and further varythe overall length of the plate.

In a preferred embodiment of the present invention, plate 600 would beprovided to the health care facility in a set of segments. For example,a set or group of six segments could include a longer and a shorter oneof first, second, and third segments 602, 604, 666. These segments couldbe assembled to cover a range of sizes. Additional intermediate segments666 can be used to assemble a plate that covers additional levels of thespine.

First end 668 of third segment 666 has similar features to secondsegment 604 including a fastener receiving recess 648, bone screwreceiving holes 626, ratchetings 652 on at least a portion of its uppersurface 638, and a tab 636. Second end 670 of third segment 666 hassimilar features to first segment 602 including a ratchetings 652 on atleast a portion of its lower surface 620 and a tab receiving recess 634.A first fastener 606 couples together first segment 602 to first end 668of third segment 666. A second fastener couples together second segment604 to second end 670 of third segment 666. Additional segments 666 maybe added for use across more than two levels of the spine. Segments 666are configured to be coupled together with first end 668 of one segment666 to second end 670 of another segment 666.

FIGS. 37–39 show a preferred embodiment of instrumentation 700 forcompressing and locking plate 600. Instrumentation 700 has a handle 702with a pair of tongs 704, 706 in moveable relationship to each. Tongs704, 706 are configured to cooperatively engage ends 624, 644 of firstand second segments, 602, 604, respectively, to shorten the overalllength of the plate and to apply a desired compressive load acrossmultiple levels of the spine. Instrumentation 700 may be used toposition plate 600 in a desired position at the fusion site during atleast a portion of the procedure for installing plate 600. An instrumentmay be used for holding the plate such as the instrumentation disclosedin the '721 patent incorporated by reference above. Instrument 700 canbe used to move segments 602, 604 toward one another and toward thirdsegment 666 to shorten the length of plate 600 and create a compressiveload across the respective disc spaces.

As shown in FIG. 38, an alternative embodiment of instrument 700′ may beused to move first or second segment 602, 604 toward third segment 666so that a compressive load may be applied to one disc space at a time.Instrument 700′ has a tong 704′ similar to tong 704 for engaging one ofends 624, 644 of first and second segments, and forked tong 707 forengaging the third segment as shown in FIG. 38.

After the desired length of plate 600 is achieved, an instrument 708having a head 710 configured to cooperatively engage fastener 606 isused to tighten fastener 606 to secure first, second, and third segments602, 604, 666 in a desired position.

FIG. 40 shows another preferred embodiment of a cervical plate 800 inaccordance with the present invention. Plate 800 is similar to plate 600except that first segment 802 is configured to receive at least aportion of the first end 868 of third segment 866 therein in a tongueand groove configuration and second end 870 of third segment 866 isconfigured to receive at least a portion of second segment 804 therein,in a tongue and groove configuration. A person of ordinary skill in theart would appreciate that other configurations of cooperatively engagingfirst and second segments 802, 804 are possible without departing fromthe intended purpose within the broad scope of the present invention.

FIGS. 41 a–41 d show preferred embodiments of locking elements forlocking bone screws in accordance with the present invention. Forexample, the bone screw locks may be in the form of a screw, a rivet, acap, or a cover. It is appreciated that any locking element for lockinga single one of the bone screws known to one of ordinary skill in theart would be within the scope of the present invention. The plate of thepresent invention preferably includes at least one bone screw lockadapted to lock to the plate only a single bone screw inserted into oneof the bone screw receiving holes. The plate of the present inventionmay include more than one bone screw lock, each lock being adapted tolock to the plate only a single bone screw inserted into one of the bonescrew receiving holes.

FIG. 41 a shows an enlarged fragmentary cross sectional view of alocking element 172 a and a bone screw 174 a. Locking element 172 athreadably engages bone screw receiving hole 126 to prevent bone screw174 a from backing out. In this embodiment, locking element 172 a locksbone screw 174 a in a fixed relationship to plate 100.

FIG. 41 b is an enlarged fragmentary cross sectional view of a lockingelement 172 b and a bone screw 174 b. Locking element 172 b threadablyengages bone screw receiving hole 126 to prevent bone screw 174 b frombacking out. In this embodiment, locking element 172 b is adapted tohold bone screw 174 b in an angular relationship to plate 100. Examplesof preferred fixed-angled single locking elements are taught byMichelson in U.S. Pat. No. 6,139,550, (the '550 patent) entitled“Skeletal Plating System,” the disclosure of which is herebyincorporated by reference herein. Locking element 172 b may also permitmovement of bone screw 174 b relative to plate 100.

FIGS. 41 c and 41 d are enlarged fragmentary cross sectional view of alocking element 172 c and bone screw 174 c in accordance with anotherembodiment of the present invention. Locking element 172 c threadablyengages bone screw receiving hole 126 to prevent bone screw 174 c frombacking out. In this embodiment, locking element 172 c is adapted tohold bone screw 174 c in an angular relationship to plate 100. Lockingelement 172 c may also permit movement of bone screw 174 c relative toplate 100. Locking element 172 c is adapted to adjustably lock bonescrew 174 c in a variable angle relationship relative to plate 100. Bonescrew 174 c preferably has a rounded head 176 c that cooperates with thebottom surface of single locking element 172 c, thus allowing screw 174c to move relative to plate 100. Examples of preferred variable-angledsingle locking elements are taught by Michelson in the '550 patent, thedisclosure of which is hereby incorporated by reference herein.

FIG. 41 e is an enlarged fragmentary cross sectional view of aself-locking bone screw 174 d in accordance with another embodiment ofthe present invention. Bone screw 174 d has thread 178 d adapted tothreadably engage bone screw receiving hole 126. The thread pattern ofthread 178 d has a tighter pitch than the thread pattern of the boneengaging thread of bone screw 174 d. The different thread pitchesprevent bone screw 174 d from backing out after installation iscompleted.

It is appreciated that various types of bone screws and single locksystems may be utilized with the plates of the present invention.

The plates of present invention may include a bone screw system thatallows the vertebrae to move toward an interposed bone graft, and eachother if necessary, instead of keeping the vertebrae apart during theoccurrence of the resorption phase of the creeping substitution process.For example, the '550 patent discloses three types of screw-plate-locksystems, which are themselves combinable with one another, as follows:(1) Passive Dynamic; (2) Self-Compressing; and (3) Active Dynamic andare incorporated by reference herein. The plate of the present inventionrequires (1) at least one fastener detachably attached to the plate topermit assembly and disassembly of two or more plate segments asdesired; and (2) at least one lock, whether separate from or part of thescrew, that is adapted to lock a single bone screw only so as to preventthe screw from backing out from the bone screw receiving hole of theplate. By way of example, FIG. 41 e shows a self-locking screw. Platessimilar to that of the present invention described herein havingnon-detachable fasteners wherein the plates are not adapted to beassembled and reassembled are being pursued in related applications.Plates similar to that of the present invention described herein havingmultilock mechanisms adapted to lock at least two bone screws asdescribed in the '550 patent are being pursued in related applications.Various methods for using and installing the plates of the presentinvention are disclosed in the '550 patent and '721 patent to Michelson,incorporated by reference herein.

It is appreciated that for any of the embodiments of the platesdescribed herein can be made of, treated, coated, combined with,comprised of, or used with any source of osteogenesis, fusion promotingsubstances, bone growth promoting materials, bone, bone derivedsubstances or products, demineralized bone matrix, mineralizingproteins, ossifying proteins, bone morphogenetic proteins,hydroxyapatite, genes coding for the production of bone, substancesother than bone, and bone including, but not limited to, cortical bone.The plates, screws, fasteners, and/or screw locks may also be combinedwith material and/or substance for inhibiting scar formation. Theplates, screws, fasteners, and/or screw locks may be combined with anantimicrobial material and/or surface treated or coated to beantibacterial and/or antimicrobial, such as for example, by a silvercoating. At least a portion of the bottom surface of the plates canpreferably have a porous, and/or textured and/or roughened surface andmay be coated with, impregnated with, or comprise of fusion promotingsubstances (such as bone morphogenetic proteins) so as to encourage thegrowth of bone along the underside of the plate from bone portion tobone portion. The textured bottom surface also provides a medium forretaining fusion promoting substances with which the bottom surfacelayer can be impregnated prior to installation. The bottom surface ofthe plate may be given the desired porous textured form by roughblasting or any other conventional technology, such as etching, plasmaspraying, sintering, and casting for example. If porous so as to promotebone ingrowth, the bottom surface is formed to have a porosity or poresize in the order of 50–500 microns, and preferably 100–300 microns.Bone growth promoting substances with which the porous, textured bottomsurface can be impregnated include, but are not limited to, bonemorphogenetic proteins, hydroxyapatite, or hydroxyapatite tricalciumphosphate. The plate, screws, fasteners, and/or bone screw locks mayinclude at least in part a resorbable and/or bioresorbable materialwhich can further be impregnated with a bone growth material so that asthe resorbable and/or bioresorbable material is resorbed by the body ofthe patient, the bone growth material is released, thus acting as a timerelease mechanism. The bioresorbable material may be, for example, atleast in part bone. The plate of the present invention may be used incombination with a spinal fixation implant such as any object,regardless of material, that can be inserted into any portion of thespine, such as but not limited to interbody spinal implants, interbodyspinal fusion implants, structural bone grafts, mesh, cages, spacers,staples, bone screws, plates, rods, tethers of synthetic cords or wires,or other spinal fixation hardware. The interbody spinal fusion implantsmay be at least in part bone, for example only, an allograft interbodybone graft. Alternatively, the spinal interbody spinal fusion implantmay be at least in part artificial. At least one of the plate, screws,fasteners, and/or bone screw locks may be, if so desired, electrifiedfor purposes of stimulating bone growth and contributing to bone fusion.

Other embodiments of the invention will be apparent to those skilled inthe art from consideration of the specification and practice of theinvention disclosed herein. It is intended that the specification andexamples be considered as exemplary only, with a true scope and spiritof the invention being indicated by the following claims.

1. A method for stabilizing at least two adjacent vertebral bodies inthe cervical human spine, comprising the steps of: providing a plate ofappropriate length adapted to overlap at least a portion of two adjacentcervical vertebral bodies anteriorly, said plate having at least a firstplate segment adapted to be attached to one of the adjacent vertebralbodies to be fused and a second plate segment adapted to be attached toanother one of the adjacent vertebral bodies to be fused, the first andsecond plate segments being in moveable relationship to one anotheralong a longitudinal axis of the plate, the first and second platesegments fastened together by a fastener being detachably attached to atleast one of the first and second plate segments so as to permitassembly of the plate segments by the surgeon and complete uncoupling ofthe first and second plate segments from one another; inserting at leasta first bone screw through the first plate segment of the plate and intoone of the vertebral bodies adjacent the disc space to be fused;inserting at least a second bone screw through the second plate segmentand into the other of the vertebral bodies adjacent the disc space to befused; locking at least one of the bone screws with at least one bonescrew lock adapted to lock to the plate only a single bone screw; andpermitting movement of the first and second plate segments attached tothe adjacent vertebral bodies relative to one another in response tomovement of the adjacent vertebral bodies.
 2. The method of claim 1,wherein the permitting step includes the step of permitting movement ofthe first and second plate segments in only a single direction towardone another.
 3. The method of claim 1, wherein the permitting stepincludes the sub-step of limiting the movement of the first and secondplate segments relative to one another to sequential increments alongthe longitudinal axis of the plate.
 4. The method of claim 1, whereinthe permitting step includes the step of causing movement of theadjacent vertebral bodies by moving the first and second plate segmentsrelative to one another.
 5. The method of claim 4, wherein the step ofcausing movement of the adjacent vertebral bodies includes the step ofgenerating a compressive load across the disc space between the adjacentvertebral bodies.
 6. The method of claim 5, wherein the permitting stepincludes the first and second plate segments being free to move towardone another.
 7. The method of claim 4, wherein the step of causingmovement of the adjacent vertebral bodies includes the step of storing acompressive load across the disc space between the adjacent vertebralbodies.
 8. The method of claim 7, wherein the permitting step includesthe first and second plate segments being in fixed relationship to oneanother.
 9. The method of claim 4, further comprising the steps ofproviding an instrument configured to cooperatively engage the fastenerand at least a portion of at least one of the first and second platesegments, and utilizing the instrument to move the fastener and thefirst and second plate segments relative to one another along amid-longitudinal axis of the plate.
 10. The method of claim 9, whereinthe utilizing step includes the sub-step of rotating the fastener atleast in part with the instrument.
 11. The method of claim 1, whereinthe permitting step occurs prior to the locking step.
 12. The method ofclaim 1 , wherein said permitting step includes the sub-step of movingthe first and second plate segments relative to one another after thestep of inserting the bone screws.
 13. The method of claim 1, whereinsaid permitting step includes the sub-step of moving The first andsecond plate segments relative to one another before the step ofinserting the bone screws.
 14. The method of claim 1, further comprisingthe step of applying a compressive load to the adjacent vertebralbodies.
 15. The method of claim 1, wherein said permitting step includesthe sub-step of applying a compressive load to the adjacent vertebralbodies.
 16. The method of claim 1, wherein the permitting step includesmoving the first and second plate segments from a first position to asecond position.
 17. The method of claim 1, further comprising the stepof tightening the fastener from a first position to a second position toresist movement of the first and second plate segments relative to eachother in at least one direction.
 18. The method of claim 17, wherein thetightening step includes resisting movement of the first and secondplate segments relative to one another when the fastener is in thesecond position.
 19. The method of claim 17, wherein the tightening stepincludes permitting movement of the first and second plate segmentsrelative to one another when the fastener is in the second position. 20.The method of claim 19, wherein the tightening step includes limitingthe movement of the first and second plate segments relative to oneanother to one direction along the longitudinal axis of the plate. 21.The method of claim 19, wherein the tightening step includes limitingthe movement of the first and second plate segments relative to oneanother to sequential increments along the longitudinal axis of theplate.
 22. The method of claim 17, wherein said tightening step includestightening said fastener to cause the fastener to tighten to the firstplate segment while permitting movement of the first and second platesegments relative to one another.
 23. The method of claim 1, furthercomprising the step of adjusting the overall length of the plate bymoving the first and second plate segments relative to each other. 24.The method of claim 1, wherein the providing step includes selecting atleast one of the first and second plate segments from a group of platesegments of various lengths.
 25. The method of claim 1, wherein theproviding step includes selecting at least one of the first and secondplate segments from a group of plate segments of various configurations.26. The method of claim 1, wherein the providing step includes providinga plate having at least a third plate segment.
 27. The method of claim26, wherein the providing step includes selecting at least one of thefirst, second, and third plate segments from a group of plate segmentsof various lengths.
 28. The method of claim 26, wherein the providingstep includes selecting at least one of the first, second, and thirdplate segments from a plurality of plate segments of variousconfigurations.
 29. The method of claim 1, further comprising the stepof combining the plate with an interbody spinal fusion implant.
 30. Themethod of claim 29, wherein the implant comprises at least in part bone.31. The method of claim 29, wherein the implant is an allograftinterbody bone graft implant.
 32. The method of claim 29, wherein theimplant is an artificial implant.
 33. The method of claim 1, furthercomprising the step of combining the plate with a fusion promotingsubstance.
 34. The method of claim 33, wherein the fusion promotingsubstance is at least in part other than bone.
 35. The method of claim33, wherein the fusion promoting substance is at least bone,hydroxyapatite, or bone morphogenetic protein.
 36. The method of claim1, wherein the providing step further comprises the step of providingbone screws for engaging the plate to the cervical spine, wherein atleast a portion of one of the plate, the at least one bone screw lock,and the bone screws is a bioresorbable material.
 37. The method of claim36, wherein the bioresorbable material is at least in part bone.
 38. Themethod of claim 1, further comprising the step of combining the platewith a substance for inhibiting scar formation.
 39. The method of claim1, further comprising the step of combining the plate with anantimicrobial material.
 40. The method of claim 1, further comprisingthe step of treating the plate with an antimicrobial material.
 41. Themethod of claim 1, further comprising the step of electrifying at leastone of the plate, the fastener, the bone screws, and the bone screw lockfor purposes of stimulating bone growth and contributing to bone fusion.42. The method of claim 1, wherein the step of providing includesproviding each of the plate segments with a length sufficient to overlapat least a portion of the adjacent vertebral bodies.
 43. The method ofclaim 1, wherein the step of inserting at least a first bone screwincludes inserting the at least a first bone screw through the plate andinto the vertebral body and the step of locking includes locking thebone screw inserted through the plate and into the vertebral body. 44.The method of claim 1, wherein the step of locking includes threading aportion of the at least one bone screw lock against a portion of theplate.
 45. The method of claim 1, wherein the at least one bone screwincludes a head, the step of locking being accomplished withoutpenetrating the head of the at least one bone screw.
 46. A method forstabilizing at least two adjacent vertebral bodies in the cervical humanspine, comprising the steps of: providing a plate of appropriate lengthadapted to overlap at least a portion of two adjacent cervical vertebralbodies anteriorly, said plate having at least a first plate segmentadapted to be attached to one of the adjacent vertebral bodies to befused and a second plate segment adapted to be attached to another oneof the adjacent vertebral bodies to be fused, the first and second platesegments being in moveable relationship to one another along alongitudinal axis of the plate, the first and second plate segmentsfastened together by a fastener being detachably attached to at leastone of the first and second plate segments so as to permit assembly ofthe plate segments by the surgeon and complete uncoupling of the firstand second plate segments from one another; inserting at least a firstbone screw through the first plate segment of the plate and into one ofthe vertebral bodies adjacent the disc space to be fused; inserting atleast a second bone screw through the second plate segment and into theother of the vertebral bodies adjacent the disc space to be fused;locking at least one of the bone screws with at least one bone screwlock adapted to lock to the plate only a single bone screw; andpermitting movement of the first and second plate segments attached tothe adjacent vertebral bodies relative to one another, the permittingstep including the step of allowing but not causing the movement of theadjacent vertebral bodies by movement of the first and second platesegments of the plate.
 47. The method of claim 46, wherein thepermitting step includes the first and second plate segments being freeto move toward one another.